Method for producing fluorine-containing alkane

ABSTRACT

The present invention provides a method for producing a fluorine-containing alkane, which comprises reacting at least one fluorine-containing compound selected from the group consisting of chlorine-containing fluoroalkanes and fluorine-containing alkenes with hydrogen gas in the presence of catalysts, wherein two or more catalysts having different catalytic activities are used, and the fluorine-containing compound and hydrogen gas, which are starting materials, are sequentially brought into contact with the catalysts in the order of the catalyst having a lower catalytic activity followed by the catalyst having a higher catalytic activity. According to the present invention, in the method for producing a fluorine-containing alkane by using chlorine-containing fluoroalkane or fluorine-containing alkene as a starting material, and subjection it to a reduction reaction or a hydrogen addition reaction, the objective fluorine-containing alkane can be produced with high productivity.

This application is a U.S. national stage of International ApplicationNo. PCT/JP2011/053551 filed Feb. 18, 2011.

TECHNICAL FIELD

The present invention relates to a method for producingfluorine-containing alkane.

BACKGROUND ART

Fluorine-containing alkane is useful for various kinds of applications,such as a reaction intermediate, foaming agent, coolant and the like.

As an example of a known method for producing fluorine-containingalkane, fluorine-containing olefin is reduced at room temperature usinga palladium catalyst (see Non Patent Literature 1 below). Another methodis also reported wherein CF₃CF═CF₂ is reduced by hydrogen through aliquid phase reaction using BaSO₄, a palladium catalyst supported onactivated carbon, etc. (see Patent Literature 1 below).

However, in order to achieve a high selectivity of the targetfluorine-containing alkane in these methods, the reaction rate needs tobe slowed down; therefore, it is impossible to producefluorine-containing olefin efficiently on an industrial scale.

Patent Literature 2 below discloses a method for producing fluorinatedpropane, through a multistep reaction, using fluorine-containing olefinas a starting material by reacting it with hydrogen or a like reducingagent in the presence of a catalyst. A preferable embodiment of thismethod is such that the reaction is suppressed using only a small amountof catalyst at the initial stage of reaction and then the amount of thecatalyst is gradually increased. It is said that this method achieves ahigh conversion rate and selectivity at a relatively high productionspeed.

However, in the method disclosed in Patent Literature 2, the amount ofheat generated by the reaction becomes unduly large; therefore, removalof heat is necessary by a method, for example, that employs a reactorequipped with a jacket and removes heat using a refrigerant, or othermeans for cooling the reaction mixture, such as the use of an internalcooling coil, introduction of a diluent into the reaction mixture foradditional cooling, and the like. This makes the structure of thereaction apparatus complicated. Furthermore, in order to avoid anexcessive temperature rise, control of the introduction speed of thestarting material compound becomes necessary, and this entails areduction in the production efficiency of the target fluorine-containingalkane.

CITATION LIST

Patent Literature

-   PTL 1: Japanese Unexamined Patent Publication No. 1996-165256-   PTL 2: Japanese Unexamined Patent Publication No. 2008-162999

Non Patent Literature

-   NPL 1: Izvest. Akad. Nauk S. S. S. R., Otdel. Khim. Nauk. (1960),    1412

SUMMARY OF INVENTION Technical Problem

The present invention has been accomplished in view of the foregoingproblems found in the prior art. A main object of the present inventionis to provide a method for producing fluorine-containing alkane withhigh production efficiency in the method of using chlorine-containingfluoroalkane or fluorine-containing alkene as a starting material, andreacting it with hydrogen gas.

Solution to Problem

The present inventors conducted extensive research to achieve theabove-described object. As a result, they found the following. Whenchlorine-containing fluoroalkane or fluorine-containing alkene isreacted with hydrogen gas to conduct a hydrogen addition reaction or areduction reaction by hydrogen, the temperature rise during the reactioncan be suppressed without reducing the conversion rate or selectivity byusing a plurality of catalysts having different catalytic activities insuch a manner that the first stage of the reaction is conducted underthe presence of the catalyst having the lowest activity followed bymultistep reactions using catalysts having sequentially higher catalyticactivity in each step. As a result, the speed of introducing thestarting materials can be increased and the production efficiency can begreatly improved. The present invention has been accomplished on thebasis of this finding.

Specifically, the present invention provides the following method forproducing fluorine-containing alkane.

Item 1. A method for producing fluorine-containing alkane comprisingreacting at least one fluorine-containing compound selected from thegroup consisting of chlorine-containing fluoroalkanes andfluorine-containing alkenes with hydrogen gas in the presence of acatalyst,

wherein two or more types of catalysts having different catalyticactivities are used, and said at least one fluorine-containing compoundand hydrogen gas, which are starting materials, are sequentiallycontacted with the catalysts in the order of lower to higher catalyticactivity.

Item 2. The method according to Item 1, which uses a reaction apparatusin which two or more reaction tubes charged with catalysts havingdifferent catalytic activities are connected in series.

Item 3. The method according to Item 1 or 2, wherein each catalyst isone containing a noble metal component supported on a carrier.

Item 4. The method according to any one of Items 1 to 3, wherein thenoble metal is at least one member selected from the group consisting ofPd, Pt, Ru and Rh, and the carrier is at least one member selected fromthe group consisting of activated carbon, porous alumina silicate,aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, zincoxide and aluminum fluoride.

Item 5. The method according to Item 3 or 4, wherein the catalystshaving different catalytic activities are those containing identicalnoble metal components supported on identical carriers with differentsupporting amounts, and the fluorine-containing compound and hydrogengas, which are starting materials, are sequentially contacted with acatalyst containing a smaller amount of noble metal component to acatalyst containing a larger amount of noble metal component.

Item 6. The method according to any one of Items 1 to 5, wherein thechlorine-containing fluoroalkane is at least one member selected fromthe group consisting of:

a compound represented by Formula (1):R¹—CCl_(2-(n+m))H_(n)F_(m)—CCl_(2-(o+p))H_(o)F_(p)—CCl_(3-(q+r))H_(q)F_(r)wherein R¹ is a alkyl group, a hydrogen atom, a fluorine atom, or a C₁₋₄fluoroalkyl group that may contain a chlorine atom(s); n, m, o and p areeach individually an integer of 0 to 2; q and r are each individually aninteger of 0 to 3, with the proviso that n+m≦2, o+p≦2, q+r≦3, andn+m+o+p+q+r≦6; provided that when R¹ is neither a fluoroalkyl group nora fluorine atom, the sum of m, p and r is 1 or greater; and

a compound represented by Formula (2):CCl_(3-(a+b))H_(a)F_(b)—CCl_(3-(c+d))H_(c)F_(d)wherein a, b, c and d are each individually an integer of 0 to 3, a+b≦3,c+d≦3, b+d≧1, and a+b+c+d≦5; and

the fluorine-containing alkene is a fluorine-containing alkenerepresented by Formula (3):R³Y¹C═CY²R⁴wherein R³ and R⁴ may be the same or different and each represents aC₁₋₄ alkyl group, a hydrogen atom, a fluorine atom, a chlorine atom, ora C₁₋₄ fluoroalkyl group that may contain a chlorine atom(s); Y¹ and Y²may be the same or different and each represents a hydrogen atom, afluorine atom or a chlorine atom; with the proviso that when R³ and R⁴are neither a fluoroalkyl group nor a fluorine atom, at least one of Y¹and Y² is a fluorine atom.

Item 7. The method according to any one of Items 1 to 6, wherein thechlorine-containing fluoroalkane is a compound represented by Formula(1-1): R²—CCl_(2-(j+k))H_(j)F_(k)—CCl_(3-(l+t))H₁F_(t) wherein R² is aC₁₋₃ alkyl group, a hydrogen atom, a fluorine atom, or a C₁₋₃fluoroalkyl group that may contain a chlorine atom(s); j and k are eachindividually an integer of 0 to 2; l and t are each individually aninteger of 0 to 3; j+k≦2; l+t≦3; and j+k+l+t≦4; with the proviso thatwhen R² is neither a fluoroalkyl group nor a fluorine atom, the sum of kand t is 1 or greater; and

the fluorine-containing alkene is a compound represented by Formula(3-1): R⁵CY³═CY⁴Y⁵

wherein R⁵ is a hydrogen atom, a C₁₋₃alkyl group, or a C₁₋₃ fluoroalkylgroup; Y³, Y⁴ and Y⁵ may be the same or different and each represents ahydrogen atom or a fluorine atom; with the proviso that when R⁵ is not afluoroalkyl group, at least one of Y³ and Y⁴ is a fluorine atom.

The production method of the present invention is explained in detailbelow.

Starting Material Compound

In the present invention, at least one fluorine-containing compoundselected from the group consisting of chlorine-containing fluoroalkanesand fluorine-containing alkenes is used as a starting material.

The chlorine-containing fluoroalkanes are not particularly limited andexamples thereof include a compound represented by Formula (1):R¹—CCl_(2-(n+m))H_(n)F_(m)—CCl_(2-(o+p))H_(o)F_(p)—CCl_(3-(q+r))H_(q)F_(r)wherein R¹ is a C₁₋₄ alkyl group, a hydrogen atom, a fluorine atom, or aC₁₋₄ fluoroalkyl group that may contain a chlorine atom(s); n, m, o andp are each individually an integer of 0 to 2; q and r are eachindividually an integer of 0 to 3, with the proviso that n+m≦2, o+p≦2,q+r≦3, and n+m+o+p+q+r≦6; provided that when R¹ is neither a fluoroalkylgroup nor a fluorine atom, the sum of m, p and r is 1 or greater; and

a compound represented by Formula (2):CCl_(3-(a+b))H_(a)F_(b)—CCl_(3-(c+d))H_(c)F_(d)wherein a, b, c and d are each individually an integer of 0 to 3, a+b≦3,c+d≦3, b+d≧1, and a+b+c+d≦5.

Among the groups represented by R¹ in Formula (1), fluoroalkyl groupsthat may contain a chlorine atom(s) include linear or branchedfluoroalkyl groups having about 1 to 4 carbon atoms that may contain upto 8 chlorine atoms. Specific examples of the fluoroalkyl groups includea perfluoroalkyl group and a fluoroalkyl group that contains 1 to 8fluorine atoms. Among the groups represented by R¹, examples of alkylgroups include a methyl group, an ethyl group, an n-propyl group, anisopropyl group, an n-butyl group, a sec-butyl group, a tert-butyl groupand like linear or branched alkyl groups.

Among the chlorine-containing fluoroalkanes represented by the aboveformula, a preferable compound is as shown below.R²—CCl_(2-(j+k))H_(j)F_(k)—CCl_(3-(l+t))H_(l)F_(t)  Formula (1-1)wherein R² is a C₁₋₃ alkyl group, a hydrogen atom, a fluorine atom, or aC₁₋₃ fluoroalkyl group that may contain a chlorine atom(s); j and k areeach individually an integer of 0 to 2; 1 and t are individually aninteger of 0 to 3; j+k≦2; 1+t≦3; and j+k+l+t≦4; with the proviso thatwhen R² is neither a fluoroalkyl group nor a fluorine atom, the sum of kand t is 1 or greater.

Examples of C₁₋₃ alkyl groups represented by R² in Formula (1-1) includea methyl group, an ethyl group, a propyl group, an isopropyl group andthe like. Examples of C₁₋₃ fluoroalkyl groups that may contain achlorine atom(s) include the aforementioned alkyl groups having 1 to 7fluorine atoms and 0 to 2 chlorine atoms substituted thereon.

Examples of chlorine-containing fluoroalkanes represented by Formula(1-1) include CH₃CF₂CH₂Cl, CH₃CH₂CF₂CH₂Cl, CF₃CH₂Cl, CF₃CHClCH₂F,CF₂ClCH₂CFClCF₃, CH₃CFClCH₃, CF₃CH₂CHClCCl₂F, CH₃CHFCFHCl,CF₃CHClCHFCF₂Cl, CClHFCH₂F and the like.

An example of a fluorine-containing alkene includes a compoundrepresented by the following formula:R³Y¹C═CY²R⁴  Formula (3)wherein R³ and R⁴ may be the same or different and each represents aC₁₋₄ alkyl group, a hydrogen atom, a fluorine atom, a chlorine atom, ora C₁₋₄ fluoroalkyl group that may contain a chlorine atom(s); be thesame or different and each Y¹ and Y² may represents a hydrogen atom, afluorine atom, or a chlorine atom; with the proviso that when R³ and R⁴are neither a fluoroalkyl group nor a fluorine atom, at least one of Y¹and Y² is a fluorine atom.

In Formula (3), examples of fluoroalkyl groups and alkyl groupsrepresented by R³ and R⁴ include the same groups as those represented byR¹. Among the compounds represented by Formula (3), a compound shownbelow is preferable.R⁵CY³═CY⁴Y⁵  Formula (3-1)wherein R⁵ is a hydrogen atom, a C₁₋₃ alkyl group, or a C₁₋₃ fluoroalkylgroup; Y³, Y⁴ and Y⁵ may be the same or different and each represents ahydrogen atom or a fluorine atom; with the proviso that when R⁵ is not afluoroalkyl group, at least one of Y³ and Y⁴ is a fluorine atom.Examples of alkyl groups and fluoroalkyl groups represented by R⁵ inFormula (3-1) are the same as those represented by R².

Specific examples of fluorine-containing alkenes represented by Formula(3-1) include the compounds represented by chemical formulae CF₃CF═CF₂,CF₃CH═CFH, CH₃CF₂CF═CH₂ and the like.

Catalyst

In the present invention, the catalyst is not particularly limited andany catalysts can be used as long as they are active in an additionreaction of hydrogen gas to an alkene compound or a hydrogensubstitution reaction of a chlorine-containing compound with hydrogengas. It is particularly preferable to use a catalyst comprising a noblemetal component supported on a carrier.

Examples of the noble metals usable as catalytic components include Pd,Pt, Ru and Rh. Examples of carriers include activated carbon, porousalumina silicate represented by zeolite, aluminum oxide, silicon oxide,titanium oxide, zirconium oxide, zinc oxide, aluminum fluoride, amixture of one or more of these carrier components, a composite of oneor more of these carrier components, which are structurally combined,and the like.

The amount of noble metal supported on the carrier is not limited, and,for example, preferably the amount of the noble metal supported is about0.001 to 50% by weight, more preferably about 0.001 to 20% by weight,and particularly preferably 0.01 to 10% by weight, based on the totalweight of the catalyst supporting noble metal.

The method for preparing the catalyst is not particularly limited. Anexample of the method for preparing a catalyst comprising a noble metalcomponent supported on a carrier is as below. That is, activated carbonor a like carrier is immersed in a solution containing a metal salt toimpregnate the carrier with the solution, if necessary, followed byneutralization, sintering or a like operation, thereby obtaining thecatalyst comprising a noble metal component supported on a carrier. Theamount of the noble metal supported can be suitably controlled byadjusting the impregnation method, such as the concentration of themetal salt in the metal salt solution, the impregnation time, and thelike.

Method for Producing Fluorine-Containing Alkane

The method of the present invention is to produce fluorine-containingalkane using at least one fluorine-containing compound selected from thegroup consisting of the aforementioned chlorine-containing fluoroalkanesand fluorine-containing alkenes as starting materials and reacting thestarting materials with hydrogen gas in the presence of a catalyst.

Among the chlorine-containing fluoroalkanes, when a chlorine-containingfluoroalkane represented by Formula (1):R¹—CCl_(2-(n+m))H_(n)F_(m)—CCl_(2-(o+p))H_(o)F_(p)—CCl_(3-(q+r))H_(q)F_(r)(wherein R¹, n, m, o, p, q and r are the same as above) is used as astarting material, a fluorine-containing alkane represented by Formula:R¹—CH_(2-m)F_(m)—CH_(2-p)F_(p)—CH_(3-r)F_(r) (wherein R¹, m, p and r arethe same as above) can be produced by a substitution reaction ofhydrogen for a chlorine atom(s). When a chlorine-containing fluoroalkanerepresented by Formula (2):CCl_(3-(a+b))H_(a)F_(b)—CCl_(3-(c+d))H_(c)F_(d) (wherein a, b, c and dare the same as above) is used as a starting material, afluorine-containing alkane represented by Formula:CH_(3-b)F_(b)—CH_(3-d)F_(d) (wherein b and d are the same as above) canalso be produced by the substitution reaction of hydrogen for a chlorineatom(s). For example, when a compound represented by Formula (1-1):R²—CCl_(2-(j+k))H_(j)F_(k)—CCl_(3-(l+t))H_(l)F_(t) (wherein R², j, k, 1and t are the same as above) is used as a starting material, afluorine-containing alkane represented by Formula:R²—CH_(2-k)F_(k)—CH_(3-t)F_(t) (wherein R², k and t are the same asabove) can be produced by a hydrogen substitution reaction.

Among fluorine-containing alkenes, when a fluorine-containing alkenerepresented by Formula (3): R³Y¹C═CY²R⁴ (wherein R³, R⁴, Y¹ and Y² arethe same as above) is used as a starting material, a fluorine-containingalkane represented by Formula: R³Y¹CH—CHY²R⁴ (wherein R³, R⁴, Y¹ and Y²are the same as above) can be produced by an addition reaction ofhydrogen gas. For example, when a fluorine-containing alkene representedby Formula (3-1): R⁵CY³═CY⁴Y⁵ (wherein R⁵, Y³, Y⁴ and Y⁵ are the same asabove) is used as a starting material, a fluorine-containing alkanerepresented by Formula: R⁵CHY³—CHY⁴Y⁵ (wherein, R⁵, Y³, Y⁴ and Y⁵ arethe same as above) can be produced.

In the method for producing fluorine-containing alkane of the presentinvention, the use of a plurality of catalysts having differentcatalytic activities is required. In this method, it is necessary toconduct a multistep reaction by contacting hydrogen gas and at least onefluorine-containing compound selected from the group consisting ofchlorine-containing fluoroalkanes and fluorine-containing alkenes with acatalyst having the lowest activity in the first stage of the reaction,followed by contact thereof with a catalyst(s) in the order of lower tohigher catalytic activity. By employing a multistep reaction method asdescribed above, wherein a plurality of catalysts having differentcatalytic activities are used and the starting materials are contactedwith a catalyst in the order of lower to higher catalytic activity, thetemperature rise during the reaction can be suppressed withoutdeteriorating the conversion rate, selectivity, and the like. This makesit possible to increase the amount of starting material supplied and togreatly improve the production efficiency of the targetfluorine-containing alkane.

The catalytic activity of the catalyst varies depending on the types ofcatalyst metal and carrier used, and the amount of the catalyst metalsupported. When identical catalyst metals and carriers are used,although there is an upper limit, there is a tendency for the catalyticactivity to rise as the amount of the catalyst metal supportedincreases. Therefore, when catalysts comprising identical noble metalcomponents are supported on identical carriers in different amounts, thefluorine-containing compound and hydrogen gas, which are startingmaterials, should be sequentially contacted with a catalyst comprising asmaller amount of noble metal component supported followed by a catalystcomprising a larger amount of noble metal component supported.

A catalyst can be made into one that has a lower catalytic activity bymixing it with an inactive substance to dilute it. An example of such aninactive substance is activated carbon, but is not limited thereto. Whencatalysts comprising different types of catalyst metal and/or carrierare used, by performing a preliminary experiment using the same startingmaterial as that actually used, the intensity of the catalytic activitycan be easily determined.

When a plurality of catalysts having different catalytic activities areused, the proportion of catalysts is not particularly limited and can besuitably selected, depending on the level of activity of the catalystused, so as to suppress the heating during reaction, to prevent anexcessive temperature rise, and to maintain the desirable conversionrate of the starting material and selectivity of the target product, aslong as it meets the requirement that the fluorine-containing compoundand hydrogen gas, which are starting materials, are made to contact witha catalyst having a smaller catalytic activity sequentially followed bythat having a higher catalytic activity. For example, the proportion ofthe catalyst used may be such that, relative to 100 parts by weight ofthe catalyst having the highest activity, the total amount of othercatalysts is about 50 to 400 parts by weight, and preferably about 70 to300 parts by weight.

The structure of the reaction apparatus is not particularly limited. Asan example of a usable reaction apparatus, two or more gas phasereactors are connected in series, wherein a catalyst having the lowestcatalytic activity is placed in the first reactor of the reactionapparatus, and catalysts having sequentially higher catalytic activitiesare placed in the second and following reactors sequentially.Furthermore, it is also possible to use a single gas phase reactor,rather than a plurality of reactors, wherein a catalyst having thelowest catalytic activity is placed near the entrance and a catalysthaving the highest catalytic activity is placed near the exit, so thatthe catalytic activities of the catalysts are sequentially arranged fromlow to high in the direction along which the starting material gasflows.

An example of each reactor usable in the reaction apparatus describedabove includes a tubular flow reactor. Examples of flow reactors includeadiabatic reactors, multi-tubular reactors that are cooled using a heattransmittance medium. Preferably, the reactor is made of a material thatis resistant to the corrosive action of hydrogen fluoride, such asHastelloy, Inconel, Monel, or the like.

Because the production method of the present invention allows heating tobe suppressed during the reaction, the target fluorine-containing alkanecan be produced at a high production efficiency without activelyperforming cooling. Fluorine-containing alkane can be efficientlyproduced by, for example, a reaction apparatus with a simple structuresuch as only having cooling fins, without having to introduce a diluentinto the reaction mixture as a coolant or use a complicated reactionapparatus provided with a jacket or an internal cooling coil.

The reaction temperature is not particularly limited but it must be setlower than the ignition point of hydrogen. The reaction temperature isgenerally about 50 to 400° C., preferably about 50 to 390° C., and morepreferably about 50 to 380° C. The production method of the presentinvention can suppress heating during the reaction; therefore, comparedto conventional methods, even in the case where the amount of startingmaterial introduced is increased, the reaction temperature can becontrolled within the above mentioned range. This allows the targetfluorine-containing alkane to be produced at a high productionefficiency.

The pressure during the reaction is not particularly limited and thereaction may be performed under reduced pressure, ordinary pressure, orthe application of pressure. Usually, the reaction may be performedunder a level of pressure that is close to atmospheric pressure (0.1MPa).

The amount of hydrogen gas used is preferably about 1 to 10 mol,preferably about 1 to 8 mol, and more preferably about 1 to 5 mol permole of the starting material, i.e., at least one fluorine-containingcompound selected from the group consisting of chlorine-containingfluoroalkanes and fluorine-containing alkenes.

The reaction time is not particularly limited and, when achlorine-containing fluoroalkane is used as the starting material, it ispreferable that the reaction time be selected in such a manner that thecontact time represented by W/Fo, i.e., the ratio of the total weight ofthe catalyst used in all stages of the reaction W (g) relative to thetotal flow rate Fo (the flow rate: cc/sec at 0° C. and 0.1 MPa) of thestarting material gases (i.e., the total amount of thefluorine-containing compound and hydrogen gas) that are supplied to thereaction apparatus, is generally about 0.5 to 60 g·sec/cc, morepreferably about 1 to 50 g·sec/cc, and still more preferably about 1 to40 g·sec/cc. Furthermore, when fluorine-containing alkene is used as thestarting material, the contact time represented by W/Fo is preferablyabout 0.5 to 30 g·sec/cc, more preferably about 0.5 to 20 g·sec/cc, andstill more preferably about 0.5 to 15 g·sec/cc.

Advantageous Effects of Invention

In terms of the method for producing fluorine-containing alkane whereinchlorine-containing fluoroalkane or fluorine-containing alkene is usedas a starting material and reacted with hydrogen gas, the presentinvention provides a method that can suppress the temperature riseduring the reaction without decreasing the conversion rate andselectivity; therefore, it can significantly improve the productionefficiency by increasing the introduction rate of the starting material.

DESCRIPTION OF EMBODIMENTS

The present invention is explained in further detail below withreference to the Examples.

Example 1

Using a reaction tube made of SUS having an inside diameter of 50 mm anda length of 128 cm, 530 g of a catalyst containing Pd supported onactivated carbon (the amount of Pd supported: 0.1% by weight (the totalamount of the carrier and Pd is defined as 100% by weight) (0.1 wt %Pd/C catalyst) was placed in the area within the range of about 10 to 70cm from the entrance of the reaction tube and 530 g of a catalystcontaining Pd supported on activated carbon (the amount of Pd supported:0.25% by weight) (0.25 wt % Pd/C catalyst) was placed in the area withinthe range of about 70 to 120 cm from the entrance. The catalysts weredried at 150° C. and reduced by flowing hydrogen at 200° C. beforehand.

After heating the reaction tube described above to about 260° C. using aheater, CF₃CF₂CH₂Cl (HCHC-235cb) and hydrogen were supplied therein at arate of 945 ml/min (the flow rate at 0° C. and 0.1 MPa, the same appliesto the following) and 1,920 ml/min respectively.

The exit gas from the reactor was analyzed by gas chromatography, withthe result that the conversion of CF₃CF₂CH₂Cl (HCFC-235cb) was 94.5% andthe selectivity of CF₃CF₂CH₃ (HFC-245cb) was 96.9%. The maximumtemperature inside the reactor was 336° C.

This method obtained the target product, i.e., CF₃CF₂CH₃ (HFC-245cb), ata rate of 865 ml/min (0.82 ml/min/g-cat).

Comparative Example 1

1,059 g of catalyst containing Pd supported on activated carbon (theamount of Pd: 0.25% by weight) (0.25 wt % Pd/C catalyst) was placed in areaction tube made of SUS having an inside diameter of 50 mm and alength of 128 cm. The catalyst was dried at 150° C. and reduced byflowing hydrogen at 200° C. beforehand.

After heating the reaction tube described above to about 260° C. using aheater, CF₃CF₂CH₂Cl (HCFC-235cb) and hydrogen were supplied therein at aflow rate of 702 ml/min and 1,991 ml/min respectively.

The exit gas from the reactor was analyzed by gas chromatography, withthe result that the conversion of CF₃CF₂CH₂Cl (HCFC-235cb) was 95.5% andthe selectivity of CF₃CF₂CH₃(HFC-245cb) was 96.7%. The maximumtemperature inside the reactor was 381° C.

This method obtained the target product, i.e., CF₃CF₂CH₃ (HFC-245cb), ata rate of 648 ml/min (0.61 ml/min/g-cat).

In Example 1 and Comparative Example 1, almost the same amounts ofcatalysts were used. However, in Example 1, the half amount thereof wasa catalyst having low catalytic activity. Comparing the results ofExample 1 to those of Comparative Example 1, the conversion rate of thestarting material and the selectivity of fluorine-containing alkane werealmost the same; however, the temperature rise in the reactor wassuppressed in Example 1 compared to Comparative Example 1. As a result,in contrast to Comparative Example 1 wherein the introduction amount ofthe starting material could not be increased, the introduction amount ofthe starting material in Example 1 could be increased, enhancing theproduction amount of the target product, i.e., CF₃CF₂CH₃ (HFC-245eb) perunit time.

Example 2

Using a reaction tube made of SUS having an inside diameter of 25 mm anda length of 140 cm, 100 g of a catalyst containing Pd supported onactivated carbon (the amount of Pd supported: 0.2% by weight) (0.2 wt %Pd/C catalyst) was placed in the area within the range of about 10 to 50cm from the entrance of the reaction tube, 100 g of catalyst containingPd supported on activated carbon (the amount of Pd supported: 0.3% byweight) (0.3 wt % Pd/C catalyst) was placed in the area within the rangeof about 50 to 90 cm from the entrance of the reaction tube, and 100 gof catalyst containing Pd supported on activated carbon (the amount ofPd supported: 0.6% by weight) (0.6 wt % Pd/C catalyst) was placed in thearea within the range of about 90 to 130 cm from the entrance of thereaction tube. The catalysts were dried at 150° C. and reduced byflowing hydrogen at 200° C. beforehand.

From the entrance of the reaction tube where the 0.2 wt % Pd/C catalystwas placed, hexafluoropropene (CF₃CF═CF₂) and hydrogen were flowed intothe reaction apparatus described above at flow rates of 1,597 ml/min and2,256 ml/min respectively. The internal temperature of the reaction tubewhen the hydrogen and hexafluoropropene were introduced was 25° C.

The exit gas from the reactor was analyzed by gas chromatography, withthe result that the conversion of hexafluoropropene was 98.9% and theselectivity of CF₃CHFCHF₂ (HFC-236ea) was 100%. The maximum temperatureinside the reactor was 268° C.

This method made it possible to obtain the target product, i.e.,CF₃CHFCHF₂(HFC-236ea), at a rate of 1,578 ml/min (5.26 ml/min/g-cat).

Comparative Example 2

270 g of catalyst containing Pd supported on activated carbon (theamount of Pd supported: 3% by weight) (3 wt % Pd/C catalyst) was placedin a reaction tube made of SUS having an inside diameter of 25 mm and alength of 120 cm, followed by ice-cooling. The catalyst was dried at150° C. and reduced by flowing hydrogen at 200° C. beforehand.

Into the reaction tube described above, hexafluoropropene and hydrogenwere supplied at flow rates of 769 ml/min and 1,662 ml/min respectively.The internal temperature of the reaction tube when the hydrogen andhexafluoropropene were introduced was 0° C.

The exit gas from the reactor was analyzed by gas chromatography, withthe result that the conversion of hexafluoropropene was 100% and theselectivity of CF₃CHFCHF₂ (HFC-236ea) was 99.6%. The maximum temperatureinside the reactor was 293° C.

This method made it possible to obtain the target product, i.e.,CF₃CHFCHF₂(HFC-236ea), at a rate of 764 ml/min (2.83 ml/min/g-cat).

In Example 2 and Comparative Example 2 described above, reactionapparatuses having almost the same size were used and the amounts ofcatalyst used were also almost the same. The difference lies in thatthree types of catalysts having different activities were used inExample 2 but a single catalyst having high activity was used inComparative Example 2.

Comparing the results of Example 2 to those of Comparative Example 2,the conversion rate and selectivity were almost the same level. However,in Comparative Example 2, regardless of the use of an ice-cooledreaction tube, the temperature significantly rose during the reaction;therefore, the introduction amount of the starting material could not beincreased. In contrast, although no ice-cooling or like active coolingwas performed, the temperature rise in the reaction tube was suppressedin Example 2. This allowed the introduction amount of the startingmaterial to be increased, enhancing the production amount of the targetproduct, i.e., CF₃CHFCHF₂ (HFC-236ea) per unit of time.

Example 3

Using a reaction tube made of SUS having an inside diameter of 25 mm anda length of 140 cm, 100 g of catalyst containing Pd supported onactivated carbon (the amount of Pd supported: 0.2% by weight) (0.2 wt %Pd/C catalyst) was placed in the area within the range of about 10 to 50cm from the entrance of the reaction tube, 100 g of catalyst containingPd supported on activated carbon (the amount of Pd supported: 0.3% byweight) (0.3 wt % Pd/C catalyst) was placed in the area within the rangeof about 50 to 90 cm from the entrance of the reaction tube, and 100 gof catalyst containing Pd supported on activated carbon (the amount ofPd supported: 0.6% by weight) (0.6 wt % Pd/C catalyst) was placed in thearea within the range of about 90 to 130 cm from the entrance of thereaction tube. The catalysts were dried at 150° C. and reduced byflowing hydrogen at 200° C. beforehand.

The reaction tube described above was heated to 150° C. using a heater,and CF₃CF═CHF (HFC-1225ye) and hydrogen were flowed at 1,032 ml/min and2,515 ml/min respectively from the entrance of the reaction tube where0.2 wt % Pd/C catalyst was placed. The internal temperature of thereaction tube was 150° C. when the hydrogen and pentafluoropropene wereintroduced.

The exit gas from the reactor was analyzed by gas chromatography, withthe result that the conversion of CF₃CF═CHF (HFC-1225ye) was 98.0% andthe selectivity of CF₃CHFCH₂F (HFC-245eb) was 99.4%. The maximumtemperature inside the reactor was 292° C.

This method made it possible to obtain the target product, i.e.,CF₃CHFCH₂F (HFC-245eb), at a rate of 1,005 ml/min.

Comparative Example 3

38 g of catalyst containing Pd supported on activated carbon (the amountof Pd supported: 3% by weight) (3 wt % Pd/C catalyst) was placed in areaction tube made of SUS having an inside diameter of 20 mm and alength of 68 cm. The catalyst was dried at 150° C. and reduced byflowing hydrogen at 200° C. beforehand.

Into the reaction tube described above, CF₃CF═CHF (HFC-1225ye) andhydrogen were flowed at flow rates of 267 ml/min and 1,065 ml/minrespectively. The internal temperature of the reaction tube whenhydrogen and pentafluoropropene were introduced was 25° C.

The exit gas from the reactor was analyzed by gas chromatography, withthe result that the conversion of CF₃CF═CHF (HFC-1225ye) was 99.5% andthe selectivity of CF₃CHFCH₂F (HFC-245eb) was 98.9%. The maximumtemperature inside the reactor was 245° C.

This method made it possible to obtain the target product, i.e.,CF₃CHFCH₂F (HFC-245eb), at a rate of 262 ml/min.

In Example 3 and Comparative Example 3 described above, reactionapparatuses with different sizes were used. Due to the large amount ofheat generated, a larger reaction apparatus could not be used inComparative Example 3. As to the catalyst, three types of catalystshaving different catalytic activities were used in Example 3, but asingle catalyst having high activity was used in Comparative Example 3.As a result, because a large amount of heat was generated by thereaction, the amount of catalyst used was limited in Comparative Example3.

Comparing the results of Example 3 to those of Comparative Example 3,they are similar in the conversion rate and selectivity, but due to theheat generated, the introduction amount of the starting material couldnot be increased in Comparative Example 3. In contrast, in Example 3,the temperature rise in the reaction tube was suppressed; therefore, theproduction amount of CF₃CHFCHF₂ (236ea) per unit of time was increased.

The invention claimed is:
 1. A method for producing fluorine-containingalkane comprising reacting at least one chlorine-containing fluoroalkanewith hydrogen gas in the presence of catalysts having differentcatalytic activities, wherein the catalysts having different catalyticactivities are: those containing Pd supported on activated carbon withdifferent supporting amounts; or those made by mixing Pd supported onactivated carbon with an activated carbon to dilute it in differentdilution rates, and wherein the at least one chlorine-containingfluoroalkane and hydrogen gas, which are starting materials, aresequentially contacted with a catalyst containing a smaller amount of Pdto a catalyst containing a larger amount of Pd.
 2. The method accordingto claim 1, wherein the reaction proceeds in a reaction apparatus inwhich two or more reaction tubes charged with catalysts having differentcatalytic activities are connected in series.
 3. The method according toclaim 1, wherein the chlorine-containing fluoroalkane is at least onemember selected from the group consisting of: a compound represented byFormula (1):R¹—CCl_(2-(n+m))H_(n)F_(m)—CCl_(2-(o+p))H_(o)F_(p)—CCl_(3-(q+r))H_(q)F_(r)wherein R¹ is a C₁₋₄ alkyl group, a hydrogen atom, a fluorine atom, or aC₁₋₄ fluoroalkyl group that may contain a chlorine atom(s); n, m, o andp are each individually an integer of 0 to 2; q and r are eachindividually an integer of 0 to 3, with the proviso that n+m≦2, o+p≦2,q+r≦3, and n+m+o+p+q+r≦6; provided that when R¹ is neither a fluoroalkylgroup nor a fluorine atom, the sum of m, p and r is 1 or greater; and acompound represented by Formula (2):CCl_(3-(a+b))H_(a)F_(b)—CCl_(3-(c+d))H_(c)F_(d) wherein a, b, c and dare each individually an integer of 0 to 3, a+b≦3, c+d≦3, b+d≧1, anda+b+c+d≦5.
 4. The method according to claim 1, wherein thechlorine-containing fluoroalkane is a compound represented by Formula(1-1):R²—CCl_(2-(j+k))H_(j)F_(k)—CCl_(3-(l+t))H_(l)F_(t) wherein R² is a C₁₋₃alkyl group, a hydrogen atom, or a fluorine atom, or a C₁₋₃ fluoroalkylgroup that may contain a chlorine atom(s); j and k are each individuallyan integer of 0 to 2; l and t are each individually an integer of 0 to3; j+k≦2; l+t≦3; and j+k+1+t≦4; with the proviso that when R² is neithera fluoroalkyl group nor a fluorine atom, the sum of k and t is 1 orgreater.